Thursday, March 3, 2011

3D Glasses: Passive Polarized Glasses and Active Shutter Glasses

3D movies are shot by recording "two" films, one for each eye, slightly displaced. To recreate the 3D effect during projection, each eye needs to see only its "own" film and not the other. There are a few technologies achieving that which we will cover in a couple of articles.

IMAX 3D, RealD 3D, Dolby 3D and XpanD 3D are the most widespread cinema theater technologies for 3D movie projection. All of these, as well as home theaters, utilize 3D glasses to make the eye see only its "own" share of the picture. 3D glasses are variations of two kinds: passive (color or polarized) glasses and active (shutter) glasses. Technically, the older anaglyph red/cyan-plastic-glued-on-white cardboard glasses that everyone has seen are also passive but they are not really used anymore because they can't produce full color images.

So what's the difference between passive polarized glasses and active shutter glasses?

Polarized glasses have a different polarizing filter on each eye. Images projected at the screen are also polarized through opposite direction filters for the left and the right eye. When coupled with the 3D glasses, this results in each glass only filtering in the corresponding image even though both are on the screen at the same time.

The color passive glasses used currently in some cinemas (notably in Dolby 3D) are in a way glorified anaglyph glasses. They show "full" color by narrowing the spectra of red, green and blue for one eye and mapping wavelengths of red, blue and green left unused from that first eye to the second eye.

Active shutter glasses take another approach. They need electricity to work, so active 3D glasses in cinema theaters usually have small batteries in them. The glass for each eye has a liquid crystal layer which can be driven either transparent or opaque by applying voltage. The projecting system alternatively shows the frame for the left and the right eye and the glasses alternatively turn the glass for the right and the left eye opaque in sync with that. The synchronization is controlled by wireless signals.

3D for home use mostly favors active shutter glasses over passive 3D glasses. LG are pretty much the only manufacturer pushing passive technology for 3D TVs and PC monitors. Runco also have proprietary passive tech for their projectors. Sony, Panasonic and Samsung are all in the active shutter glasses camp. And they all have teamed with RealD to jointly develop 3D technologies.

So what is the necessary equipment for watching 3D movies at home?

A strangely popular misconception is that pre-existing (old) Blu-ray players don't play 3D movies. An older Blu-ray player will generally only need a firmware update in order to be able to play 3D Blu-ray movies. No hardware changes are required. Most bluray player manufacturers have already released firmware updates for their players. Pretty much all software Blu-ray players also have 3D support in their latest versions. Additionally, no special HDMI cables are needed. Any high speed HDMI cable will do. That is, if a cable can transfer 1080p, then it will also transfer 3D. So the only special necessity is the 3D capable TV (or monitor, or projector) with 3D glasses.